室溫下金屬鍍膜氮化鎵之手性結構之雷射特性

Abstract

本論文中，我們於室溫下金屬塗層氮化鎵之手性結構中觀測到雷射訊號的表現，並展現其雷射訊號具有旋光偏振態之可能性。 首先我們選擇鏡像之螺旋圖形作為手性結構的設計，並利用有限元法近似解的模擬工具進一步找尋合適的元件尺度，而在製程方面，我們利用電子束微影技術在未參雜的氮化鎵材料上定義出左旋與右旋兩種互為手性圖形之螺旋結構，接著將氮化矽介電質材料與鋁金屬塗佈在此結構表層。元件製作完成後，我們使用掃描式電子顯微鏡去確認手性結構元件的週期、寬度與深度是否與我們所設計的結構尺寸相同。此後，由微光激發螢光量測系統對樣品進行量測，從實驗結果中我們觀察到兩種螺旋結構皆有一波長約三百六十四奈米的單一模態雷射訊號。由實驗與模擬結果，我們相信此雷射模態是由於表面電漿的模態與波導模態的混和所達成的。 第二個主題部分，我們利用可調變波長之四分之波片以及線性偏振片來區分左旋以及右旋結構之圓偏振特性，經過計算非對稱因子，發現元件產生雷射光之旋光程度雖不及純圓偏振光源，但已有相當程度的左右旋光性。隨後，我們利用線性偏振以及圓偏振兩種不同的偏振光源來激發我們的樣品，發現金屬塗層氮化鎵之手性結構在圓偏振光激發的條件下有著較低的閥值能量密度。綜合以上研究結果，我們相信此金屬塗層之手性結構雷射具有在小尺度的體積下產生不同圓偏振雷射光的可能性。

In this thesis, we observe the lasing action of metal-coated GaN chirality structures at room temperature and show the possibility of emitting circularly polarized light. In the first part of this thesis, we use finite element method to design the chirality structure. Then, we define the chirality pattern on the undoped GaN by e-beam lithography. After that, we deposit the Si3N4 dielectric layer and coat the aluminum on it. Next, we use scanning electron microscope to check the period, width and height of chirality structure. We observe a lasing mode from the metal-coated GaN chirality structure at 364 nm by micro-photoluminescence system. From the experiment and simulation results, these phenomenon indirectly prove the metal-coated chirality structure exist a plasmonic circularly polarized mode. In the second part, we utilize a tunable quarter-plate and a linear polarizer to analyze the polarization of chirality structures. We successfully distinguish the polarization difference between left and right chirality structure and then measure the dissymmetry factor of both lasers. Although the dissymmetry factors of our devices are not as high as the pure circularly polarized light source, they are still competitive compared with other research. Then, we compare the threshold pump power density between different metal coated structures under linearly and circularly polarized pumping condition. We find that the chirality structure has a lower threshold under circularly polarized pumping condition. These results give a promise to develop a compact size and circularly polarized nanolaser in the future.